1. Field of the Invention
The present invention relates generally to medical devices for monitoring the flow of breathing-gases through a gas delivery cannula, and more specifically the invention relates to a personal, disposable, and wearable flow indicator for monitoring the flow of a breathing-gas through a gas delivery cannula.
2. Definitions
The definitions set forth here are provided in order to clarify certain terms used in this disclosure. Examples, where provided, are not meant to limit the scope of the invention, but are provided to illustrate the relevant terms.
Breathing-gas—gaseous oxygen, either alone or admixed with other gases and/or pharmacological agents, that is or is intended to be delivered to the airway of a patient. Air, and more specifically compressed air, is considered a breathing-gas within the scope of the present disclosure and claims.
Patient—An individual who is in need of and/or who consumes a breathing-gas. The term “patient” is used herein not to limit the scope or context of the invention, but rather to emphasize that the most common use of the present invention is within the medical setting.
Personal—“Personal” when used herein refers to those collective characteristics of a flow indicator that allow the flow indicator to be used by a single patient and then disposed of. Such characteristics, as described in detail below, include the ability to easily swap the flow indicator in and out of the breathing-gas delivery system, and the ability to mass produce sufficiently large numbers of the flow indicators that they can be used and disposed of economically.
Breathing-gas source—A breathing-gas source is considered herein to be any device feeding breathing-gas under positive pressure into a gas delivery cannula, as “gas delivery cannula” is defined below. Common examples of breathing-gas sources include a tank containing a breathing-gas under pressure, and a pump that pumps a breathing-gas into a gas delivery cannula. “Breathing-gas source” as used herein includes hardware components “upstream” of the gas delivery cannula, for instance, regulators, meters, metal conduits, and “Christmas tree” connectors. For the purposes of the present disclosure, a gas outlet built into a wall or bulkhead is considered a component of a breathing-gas source.
Proximal and distal—The terms “proximal” and “distal” are used herein with reference to the patient. “Proximal” means towards or near the patient. “Distal” means away from the patient; i.e. towards, at, or near the gas source.
Airway Interface Device (AID)—A device for introducing a breathing-gas into a patient's airway. By way of example, commonly employed AID's include face masks, mouthpieces, nasal cannulas, and endotracheal tubes. An AID may be reversibly separable from the gas delivery cannula or it may be integrated into the gas delivery cannula.
Gas delivery cannula—tubing used to transmit a breathing-gas from a gas source to an AID. Flexible, transparent tubing having an internal diameter of approximately 2.0-4.0 mm is generally used as gas delivery cannulas. However, the term “gas delivery cannula” is used broadly in the present disclosure and claims to include any tubing used to transmit breathing-gas from a gas source to an AID.
Nasal cannula—a specific type of AID that delivers breathing-gas to a person's nasal passages. By way of example, the standard nasal cannula now commonly used consists of tubing that connects at its distal end to the proximal end of the gas delivery cannula and bifurcates to form a loop. The loop incorporates a nose-piece with two outlet ports. The outlet ports are placed adjacent to the patient's nares so that breathing-gas flows out of the outlet ports and directly into the nasal airway of the patient. The nasal cannula is held in place by the loop being placed over the patient's ears, by means of an elastic strap, or by other means not pertinent to the present invention.
Accommodate frictional faying—refers to a characteristic of two elements such that they are designed and manufactured with sufficiently complimentary dimensions and geometry to permit them to be frictionally joined in a secure, air-tight manner.
3. Prior Art
A very common medical situation is one in which it is necessary to deliver a breathing-gas to a patient's airway. A large variety of breathing-gas delivery systems have been designed for this purpose. Although the prior art of such breathing-gas delivery systems is too extensive to inventory here, U.S. Pat. No. 4,188,946 to Watson and Rayburn discloses a representative example.
Such breathing-gas delivery systems comprise a minimum of three elements: 1) a source of the breathing-gas; 2) a gas delivery cannula for transmitting the breathing-gas from the source to the patient, and 3) an AID for introducing the breathing-gas into the patient's airway. Many breathing-gas delivery systems incorporate additional elements incorporated into the breathing-gas source or interposed between the breathing-gas source and the gas delivery cannula. Such elements include metal conduits, “Christmas tree” connectors, wall outlets, flow meters, valves, flow regulators, and the like.
In breathing-gas delivery systems the distal end of the gas delivery cannula is connected to the breathing-gas source. The proximal end of the gas delivery cannula is continuous with or connected to the AID, which introduces the breathing-gas to the patient's airway. As long as breathing-gas is flowing through the system, the patient inhales the delivered breathing-gas as it exits the AID. If the flow of the breathing-gas through the system is cut off, the patient inhales either nothing or only ambient air, which may not have a sufficiently high oxygen content to sustain the patient. Consequently, it is important to be able to ascertain whether or not breathing-gas is flowing all the way through the gas delivery cannula to the patient's airway.
Flow-indicators are commonly used to determine whether breathing-gas is flowing in a breathing-gas delivery system. A common type of flow indicator is a rotary sight flow indicator, which comprises a rotatable member positioned in a chamber that is in communication with the gas source. The rotatable member in the chamber is visible through a window in the flow indicator housing. Gas moving through the chamber causes the rotatable member to rotate, and this provides a visible indication that the gas is moving. A representative general-use rotary sight flow indicator is disclosed by U.S. Pat. No. 4,745,877 to Chang. Such flow indicators are used in breathing-gas delivery systems. For instance, U.S. Pat. No. 6,386,196 (“Culton” herein) issued to Steven Culton discloses a rotary sight flow indicator incorporated into the flow meter hardware of breathing-gas source.
4. Problems and Limitations of the Prior Art Overcome by the Present Invention
In situations where breathing-gas delivery systems are employed to deliver breathing-gases to patients who are dependent on the breathing-gases, a failure of the system can cause catastrophic results; consequently, the prior art discloses a wide variety of flow-meters and flow indicators. These prior art devices, however, are invariably positioned at or near the source of the breathing-gas; i.e., distal to the gas delivery cannula. The Culton flow-indicator is a good example of a flow-indicator being positioned at the distal end of the system, upstream from the gas delivery cannula. Culton is actually incorporated into the gas source apparatus. Such prior art flow-indicators present a number of problems, some of which are potentially life-threatening, that are overcome by the present invention.
One such problem is that the distally placed flow indicator device can be hidden from the patient because the device is often mounted on a wall, usually behind the patient and often occluded by hanging drapes or other obstructions. Even when those who are caring for the patient can see the flow indicator, the patient himself often cannot. Similarly, flow indicator devices are often connected to portable gas tanks or pumps. Such tanks and pumps are often kept out of the way by placing them on the floor, under the bed, or behind furniture or other obstructions; consequently, it is often hard or impossible to see such flow indicators.
This problem of the patient not being able to see the flow indicator is exacerbated by the fact that many such patients do not have the strength or agility to twist around to see the flow indicators. Because the patient cannot monitor the flow-indicator, should the flow of the breathing-gas flow be interrupted, the patient may not realize it. This is particularly problematic for debilitated patients, who are most in need of a constant flow of breathing-gas.
The present invention solves this problem by providing a breathing-gas flow indicator positioned at or near the proximal end of the gas delivery cannula close to the patient's face, so that the patient and his care-givers can easily see the flow indicator and determine whether breathing-gas is flowing through the gas delivery cannula.
A second potentially dangerous problem of the existing art that is overcome by the present invention is that the distally placed flow indicators are too far “upstream” from the patient to detect flow-failures in most of the system. The amount of information provided by the flow indicator is directly proportional to the distance the flow indicator is from the gas source. In a hospital setting, the length of the gas delivery cannula between the prior art flow indicator and the patient may be several meters. If the gas delivery cannula develops a leak, or a kink, or is severed at some point between the prior art flow indicator located at the gas source and the patient, the prior art flow indicator continues to indicate that the breathing-gas is flowing normally when, in fact, the patient is not receiving any breathing-gas at all. This problem is referred to here as a “false flow signal.”
The present invention solves this false flow signal problem by providing a flow indicator placed at or near the proximal end of the gas delivery cannula, near the patient, so that any interruption of flow in the system anywhere between the patient all the way back to and including the gas source is immediately and easily detected.
A third problem with the prior art that is overcome by the present invention is that the prior art flow indicators cannot be easily retrofit into existing systems. The present invention solves this problem by providing a flow indicator that can be easily retrofit into an existing-gas delivery cannula without fittings, clamps, or other hardware. Even if the gas delivery cannula is continuous with the AID, the present invention can be easily frictionally spliced into a convenient point in the gas delivery cannula for easy viewing by the patient.
A fourth problem of the prior art that is overcome by the present invention is that the complexity of the prior art requires excessive manufacturing costs which militate against 1) the device being disposable and 2) wide-spread use and acceptance of the prior art flow indicators. The present invention solves this problem by providing a flow indicator that is sufficiently simple, elegant, and inexpensively produced that it can be widely used to improve the safety of breathing-gas delivery systems. In fact, the present invention can be inexpensively produced in such large quantities as to be used by a single patient for a brief time and then hygienically disposed of. The device can either be manufactured as a separate flow indicator that can be retrofitted into an existing-gas delivery cannula and simply replaced with each new patient, or it can be manufactured as an integral part of the gas delivery cannula, and the entire gas delivery cannula and flow indicator combination replaced when necessary. Thus, the present invention is both personal, in that it is used by only one patient, it is hygienic, and it is disposable.
A fifth problem with the prior art that is overcome by the present invention is that flow indicators incorporated into the breathing-gas source are not portable. This is of concern when a patient is transported from one location to another because during transport the distal end of the gas delivery cannula must be disconnected from the breathing-gas source (and its integrated flow indicator) and re-connected to a portable source of breathing-gas. Consequently, a separate flow indicator is required for the portable breathing-gas source. This problem is solved by the present invention by providing a flow indicator that remains interposed between the AID and the proximal end of the gas delivery cannula when the distal end of the gas delivery cannula is repeatedly connected to and disconnected from different breathing-gas sources. The invention is light enough that it can be worn by an ambulatory patient and still remain fully functional. Even if the patient walks about with a portable tank of gas, the flow indicator remains with the patient to monitor the gas flow.
A sixth problem with the prior art that is overcome by the present invention is that prior art flow indicators cannot be used at night or by the sight impaired. The present invention overcomes this problem in two ways. First, the flow indicator is worn close to the patient's face and can be raised to his eyes and observed in dim light. Second, the flow indicator vibrates gently when gas is flowing through it and the patient can feel these vibrations thereby indicating gas flow even in a completely dark room and even when used by blind patients.
5. Overview of the Invention
Our invention is a flow indicator used in a breathing-gas delivery system, the system comprising a breathing-gas source, an AID, and a gas delivery cannula for conducting breathing-gas from the source to the AID. The gas delivery cannula has a distal end in communication with the source, and a proximal end. The flow indicator has a housing that has at least one transparent housing surface. The housing forms a chamber through which the breathing-gas flows. The housing forms at least one inlet through which the breathing-gas enters the chamber and which is in direct communication with the proximal end of the gas delivery cannula. The housing also forms an outlet through which the breathing-gas exits the chamber, and which is in communication with the AID. The flow indicator has a rotatable member rotatably mounted by mounting means within the chamber and visible from without the chamber through the transparent housing surface. The rotatable member has at least one rotatable member surface upon which the flowing gas impinges and causes the rotatable member to rotate about its axis of rotation, thereby producing a visible and/or vibrational indication that the breathing-gas is flowing through the gas delivery cannula. Details, variations, and embellishments of the invention are disclosed below.